1. Field of the Invention
The present invention relates to a method of producing a poly(ortho-methylphenol), and more specifically relates to a production method to easily obtain, at high purities and yields using industrial processes, a poly(ortho-methylphenol) useful as a material for liquid crystal polyester resin, polyarylate resins, polycarbonate resins, epoxy resins and other synthetic resins offering high heat resistance and good molding property, as well as materials for high-functional compounds such as liquid crystal display elements and photo-resists.
2. Description of the Related Art
Among the conventional methods of producing a polymethylphenol, methods known to produce bispoly(methylphenol) include one relating to the production of 4,4′-dihydroxy-3,3′-dimethyldiphenyl ether, wherein 4,4′-dihydroxyphenyl ether is used as a raw material, which is formylated and then methylated to obtain the target, or 4,4′-dihydroxy phenyl ether is alkylated, formylated, methylated and then finally dealkylated to obtain the target (Japanese Patent Laid-open No. 2003-238470). However, the aforementioned method requires a long, complex process, and the yield of the target is low.
Meanwhile, a method to produce dimethyl-dihydroxydiphenyl ether is known, wherein 2-methylhydroquinone is used as a raw material, which is dehydrated and dimerized in the presence of a montmorillonite catalyst to obtain the target (Japanese Patent Laid-open No. Sho 49-55635).
Similarly as a method to produce dimethyl-dihydroxydiphenyl ether, one wherein 2-methylhydroquinone is dehydrated and dimerized in the presence of a synthetic mica catalyst to obtain the target is known (Japanese Patent Laid-open No. Sho 59-206326). However, the aforementioned methods require expensive materials and offer low conversion ratios, and the target is obtained only as a mixture containing isomers.
Furthermore, a method to produce 3,3′-dimethyl-4,4′dihydroxybenzophenone is presented in the Journal of American Chemical Society, Vol. 61, 2664 (1961), in which orthocresol phthalein is used as a raw material, which is alkali hydrolyzed with KOH to obtain the target. However, the aforementioned method also requires an expensive material that cannot be easily produced through industrial processes, and the yield is low.
Also among methods to produce trispoly(methylphenol), a method to produce 3,3′,3″-trimethyl-4,4′,4″-trihydroxyphenylmethane is presented in the Journal of American Chemical Society, Vol. 47, 2022 (1925), in which orthocresol and carbon tetrachloride are used as raw materials, which are reacted with each other in the presence of a zinc chloride catalyst to obtain 3,3′,3″-trimethylaurine (O-Cresaurin) and then this compound is reduced to finally obtain the target. However, the aforementioned method requires a long process, and the yield of the target is low. Therefore, none of the methods described above provides an economical production method that can be used advantageously in industrial processes to produce poly(ortho-methylphenol).